The invention relates to a packing device that permits removal of the primary seals, bearings and gland housing while the self-adjusting pressure energized packing remains exposed to pressurized fluid with the valve in any position.
Packings around rotating shafts are used in valves and pumps for example to seal off the shafts from leakage of pressurized fluids. Typically, the shaft extends outward of the valve or pump in order to locate drive mechanisms such as electric motors or manual valve wheels externally.
For example, a typical valve includes a valve body with flow inlet and outlet, where the body includes an internal journal bearing located in a bonnet mounted to the valve body. A valve stem is rotationally supported transverse the flow direction within the body or bonnet usually on bearings and a movable disc is threadedly connected on the other end of the valve stem such that when the stem is rotated using a handle or motor, the disc will lift or rotate to open and close the flow passage.
In order to prevent pressurized fluid or gases from leaking out of the valve body through the bonnet adjacent to the rotatable shaft, an annular space is filled with self-adjusting packing compressed around the valve stem shaft with a packing gland to seal between the stem and the bonnet.
However, due to wear and inevitable deterioration of the seals, leaks can developed and the seals are replaced. Also, during preventive maintenance activities seals are regularly replaced before problems can occur. In addition, major difficulty is presented in that pressurized fluid or gas can leak out past the shaft while the packing is being replaced. Particularly, in critical services such as gas pipelines, oil valves, critical water pumps and other machinery, it is highly undesirable to remove the valve or pump from service simply to replace the packing.
In other cases, the bearings (typically located internally and exposed to the flowing media) that rotatably support the shaft or valve stem deteriorate and require replacement or inspection. In such cases, it is also highly desirable to replace the bearings without having to shut off the valve or pump from pressurized fluid access.
U.S. Pat. No. 5,732,731 to Wafer provides a secondary sealed bypass valve for gate valves, which in effect includes an inner auxiliary packing and an outer main packing. This enables bearings and the main packing (outer packing in the bonnet) to be replaced while the temporary inner packing contains pressurized fluids such that leakage does not occur. In normal operation however, the inner packing is bypassed and the outer packing is used for the primary purpose of sealing the rotatable valve stem.
A disadvantage of the Wafer system, of course, is the additional mechanical complexity of providing two separate packings, as well as the necessary axial extension of the bonnet and the valve stem to accommodate the extra length of the valve stem and packings required. Further, such auxiliary or secondary packing require adjustment and eventually deteriorate. As a consequence the valve must be removed from service to replace the inner or auxiliary packing in any case. The provision of a secondary seal therefore in U.S. Pat. No. 5,732,731 to Wafer merely delays the inevitable complete shut down of the valve for service to replace bearings and packing.
U.S. Pat. No. 4,556,076 to Bridges provides a fire resistant valve that includes a secondary seal against pressurized fluid in what is commonly known as a xe2x80x9cbackseatedxe2x80x9d valve. An extended flange on the valve stem has a conical sealing surface, which when rotated upwardly engages a conical valve seat in the bonnet providing a metal-to-metal sealing arrangement which is highly useful in emergency situations when the heat from a fire will deteriorate packing and enable the pressurized flammable fluids from within the valve to escape up the valve stem. Backseating arrangements are not only restricted to emergency situations but can also be useful in sealing the valve during replacement of the bearings and primary packing. However, backseating only works when the valve is fully opened or in one position.
A disadvantage of relying on backseating however is that the metal-to-metal contact surfaces can become corroded or pitted. Leakage can occur past such damaged surfaces during replacement of the packing. Such leakage is particularly dangerous in gas or oil pipelines where explosive fumes, poisonous gases, etc. can escape and contaminate the area adjacent to the valve endangering workers and others in the adjacent areas. In addition, the provision of backseated components adds mechanical complexity and cost to the valve.
It is an object of the present invention to provide secondary packing for a shaft seal or valve stem seal that enables shaft bearings and primary O-ring seals on the gland housing to be removed or inspected while the valve or pump remains under full operational fluid pressure such that the pressure energized self adjusting packing seals against the shaft or valve stem automatically.
It is a further object of the invention to provide a pressure energized constantly live loaded and self-contained packing, which enables removal of the bearings, primary seals and gland housing without leakage of pressurized fluid.
It is a further object of the invention to provide a pressure energized packing that automatically adjusts and compensates for removal of gland housing, primary seals and bearings and engages the shaft or valve stem in such a manner that leakage of pressurized fluid is prevented.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.
The invention provides a packing device that permits removal of the gland housing with primary seals and bearings while the secondary seal packing remains exposed to and containing the pressurized fluid. The packing device provides for sealing a longitudinal shaft against leakage of a pressurized fluid, having an elongate valve housing with an annular internal chamber about a coaxial rotatable shaft. The chamber has an inner end with an annular stationary packing support shoulder exposed to pressurized fluid and an outer end with an annular packing access opening exposed to ambient air pressure. Annular self-travelling pressure energized retained chevron packing is disposed within the chamber, an inner end thereof engaging the stationary packing support shoulder. An axially slidable ring engages an outer end of the packing, and gland housing with O-ring primary seals and rotary bearings engage an outer end of the slidable ring. The gland housing with primary seals include compression mountings for loading the secondary seal packing. For limiting the axial movement of the ring within the chamber when the gland housing is removed, the valve housing includes an annular groove within which a floating retaining clip is slidably disposed.
Further advantages of the invention will be apparent from the following detailed description and accompanying drawings.